Contact charging member, image forming unit including the contact charging member and electrophotographic image forming apparatus including the image forming unit

Abstract

A roller-shaped contact charging member which is in contact with and electrically charges a photosensitive drum is provided on a center shaft, and includes a roller-shaped conductive foam material portion covering the shaft, and a tubular-shaped conductive resin material portion covering the foam portion. The foam portion has an electric resistance of 9×10 5 Ω or less, the resin portion includes conductive agents and has a surface electric resistance in a range from 1×10 5 Ω/□ or more to 9×10 7 Ω/□ or less, and a hardness of the charging roller as a whole is Asker F 90° or less. An image forming unit includes the charging member and the drum. An electrophotographic image forming apparatus supplies a recording paper to the unit, transfers an image from the drum to the paper, and discharges the image-transferred paper.

We claim: 
     
       1. A contact charging member provided on a center member, comprising: a conductive foam material portion covering the center member and having an electrical resistance of 9×10 5  Ω or less; and   a conductive resin material portion covering the conductive foam material portion and in contact with a member to be charged by the contact charging member, the conductive resin material portion including conductive agents and having a surface electrical resistance between 1×10 5  Ω/□ and 9×10 7  Ω/□, and   a hardness of the contact charging member being Asker F 90° or less.   
     
     
       2. A contact charging member according to claim 1, wherein: the conductive foam material portion has a roller-shape,   the conductive resin material portion has a tubular-shape, and   the contact charging member has a roller-shape.   
     
     
       3. A contact charging member according to claim 2, wherein: the member to be charged is an image carrier including a surface having an image formation area on which an image is formed and image-free areas arranged outside of the image formation area,   the tubular-shaped conductive resin material portion has both ends corresponding to the image-free areas of the image carrier and is fixed at both ends to the roller-shaped conductive foam material portion by an adhesive.   
     
     
       4. An image forming unit comprising: an image carrier; and   a contact charging member which is in contact with a surface of the image carrier and electrically charges the surface of the image carrier uniformly,   the contact charging member being provided on a center member and including   a conductive foam material portion which covers the center member and has an electrical resistance of 9×10 5  Ω or less, and   a conductive resin material portion which covers the conductive foam material portion and is in contact with the image carrier, the conductive resin material portion including conductive agents and having a surface electrical resistance between 1×10 5  Ω/□ and 9×10 7  Ω/□, and   a hardness of the contact charging member being Asker F 90° or less.   
     
     
       5. An image forming unit according to claim 4, wherein: the conductive foam material portion of the contact charging member has a roller-shape,   the conductive resin material portion of the contact charging member has a tubular-shape,   the contact charging member has a roller-shape, and   the image carrier has a drum-shape.   
     
     
       6. An image forming unit according to claim 5, wherein: the image carrier includes a surface having an image formation area on which an image is formed and image-free areas arranged outside of the image formation area,   the tubular-shaped conductive resin material portion has both ends corresponding to the image-free areas of the image carrier and is fixed at both ends to the roller-shaped conductive foam material portion by an adhesive.   
     
     
       7. An image forming unit according to claim 5, wherein the drum-shaped image carrier is rotatably driven, and the roller-shaped contact charging member is rotated by the rotation of the drum-shaped image carrier through friction produced between the surface of the conductive resin material portion of the roller-shaped contact charging member and that of the drum-shaped image carrier. 
     
     
       8. An image forming unit according to claim 5, wherein the image carrier includes an aluminum drum having an anodized aluminum layer provided on an outer surface thereof and a photosensitive material layer provided on the anodized aluminum layer. 
     
     
       9. An electrophotographic image forming apparatus, comprising: an image carrier which includes a photosensitive drum having a cylindrical surface;   a roller-shaped contact charging member which is in contact with the cylindrical surface of the photosensitive drum and electrically charges the cylindrical surface of the photosensitive drum uniformly;   an exposure device which exposes the uniformly charged cylindrical surface of the photosensitive drum with a desired image;   a developing device which develops the exposed desired image on the cylindrical surface of the photosensitive drum;   a recording medium supply device which supplies a recording medium toward the developed desired image on the cylindrical surface of the photosensitive drum;   a transfer device which transfers the developed desired image from the cylindrical surface of the photosensitive drum to the supplied recording medium; and   a recording medium discharge device which discharges the recording medium on which the developed desired image has been transferred, from the cylindrical surface of the photosensitive drum,   the roller-shaped contact charging member being provided on a center member and including: a roller-shaped conductive foam material portion which covers the center member and has an electrical resistance of 9×10 5  Ω or less; and   a tubular-shaped conductive resin material portion which covers the conductive foam material portion and is in contact with the image carrier, the conductive resin material portion including conductive agents and having a surface electrical resistance between 1×10 5  Ω/□ and 9×10 7  Ω/□, and   a hardness of the contact charging member being Asker F 90° or less.     
     
     
       10. An electrophotographic image forming apparatus according to claim 9, wherein: a cylindrical surface of the photosensitive drum has an image formation area on which an image is formed and image-free areas arranged outside of the image formation area,   the tubular-shaped conductive resin material portion of the roller-shaped contact charging member having both ends corresponding to the image-free areas of the photosensitive drum and is fixed at both ends to the roller-shaped conductive foam material portion by an adhesive.   
     
     
       11. An electrophotographic image forming apparatus according to claim 9, wherein: the photosensitive drum is rotatably driven, and the roller-shaped contact charging member is rotated by the rotation of the photosensitive drum through friction produced between the surface of the conductive resin material portion of the roller-shaped contact charging member and the cylidrical surface of the photosensitive drum.   
     
     
       12. An electrophotographic image forming apparatus according to claim 9, wherein the photosensitive drum includes an anodized aluminum layer provided on an outer surface thereof and a photosensitive material layer provided on the anodized aluminum layer.